Academic journal article Bulletin of the World Health Organization

Determining Median Urinary Iodine Concentration That Indicates Adequate Iodine Intake at Population Level

Academic journal article Bulletin of the World Health Organization

Determining Median Urinary Iodine Concentration That Indicates Adequate Iodine Intake at Population Level

Article excerpt

Voir page 635 le resume en francais. En la pagina 636 figura un resumen en espanol.

Introduction

In 1990, 1572 million people suffered from iodine deficiency, which meant it was the leading cause of preventable mental retardation. Universal salt iodization (USI)--a policy in which all salt used in agriculture, food processing, catering and households is iodized--is the agreed strategy for achieving iodine sufficiency (1). The last decade saw enormous efforts and investments towards achieving this goal, which is now within reach, and the achievements are an unprecedented public health success in the field of noncommunicable diseases (2).

The concentration of iodine in the urine (urinary iodine concentration) is the prime indicator of a person's nutritional iodine status; it is the primary variable used to measure the success of iodine supplementation in a population (1). According to current recommendations produced by the World Health Organization (WHO), United Nations Children's Fund (UNICEF) and International Council for Control of Iodine Deficiency Disorders (ICCIDD), median urinary iodine concentrations of 100-199 [micro] g/l in samples .from schoolchildren or adults indicate adequate iodine intake and optimal iodine nutrition (Table 1) (3). This recommendation was made on the basis of the assumption that the threshold of 100 [micro] g/l would allow values <50 [micro] g/l (concentrations that indicates persistent, at least moderate iodine deficiency in the population) in no more than 20% of the population. Some participants at a meeting in 1999 convened by WHO to revise the indicators felt that 20% represented an unacceptably high number of people, and the group considered raising the threshold for the median above the current value of 100 [micro] g/l (3).

It appeared, however, that this concern was not scientifically based, because no hard data were available on the frequency of concentrations of urinary iodine <50 [micro] g/l in populations where the median urinary is >100 [micro] g/l. Such iodine-replete populations could be found in areas where iodine deficiency has never existed, because of adequate food habits--such as Japan or coastal populations in Latin America, for example--or in areas previously affected by iodine deficiency disorders (IDD), where programmes of USI have been implemented successfully.

This study aimed to describe the frequency distribution of urinary iodine concentrations in iodine-sufficient populations (schoolchildren and adults). More specifically, we aimed to evaluate in such populations the proportion of people with concentrations of urinary iodine <50 [micro] g/l.

Methods

We sent a questionnaire to 29 groups of scientists around the world who we thought might have access to the appropriate data. The questionnaire asked each investigator to give a detailed description of the iodine-sufficient area that they had investigated:

--possible past history of iodine deficiency and endemic goitre;

--possible programmes of iodine supplementation and present evidence for normal concentrations; or

--normalized iodine nutrition of the population (prevalence of goitre by palpation, by ultrasounds, blood tests, results of neonatal thyroid screening).

The questionnaire also asked for a description of the populations being studied (characteristics such as number of subjects, age and sex), the mean and median urinary iodine concentrations in the population and the frequency of values below the cut-off values of 100, 50 and 20 [micro] g/l, respectively. These cut-tiff values correspond to degrees of iodine deficiency defined as moderate, mild and severe (1, 3).

Nineteen groups sent replies with adequate data. These groups constitute ,the ICCIDD Working Group and are coauthors of this study.

Results

We received responses about 48 populations in 17 countries across four continents. …

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